P1118
ChryslerThe P1118 code indicates that the Powertrain Control Module (PCM) has detected a voltage signal from the Manifold Absolute Temperature (MAT) circuit that is lower than the expected operating range.
Medium SeverityThis code means the engine's computer isn't getting a strong enough signal from the Manifold Absolute Temperature (MAT) sensor, which is like its thermometer for the air entering the engine. When the computer doesn't know the air temperature accurately, it can't correctly calculate the fuel mixture, potentially affecting how the engine runs and its fuel efficiency.
⚠️ Before You Begin (Safety First)
Before you start any work, make sure the engine is cool to the touch to avoid burns. Always remember to disconnect the negative terminal of your battery before working on any electrical components to prevent accidental shorts or shocks. Wear safety glasses to protect your eyes from debris or fluids.
Common Symptoms
- Check Engine Light is on
- Engine may run rough or hesitate, especially during cold starts
- Poor fuel economy
- Engine may exhibit rich or lean running conditions
- Difficulty starting the engine
- Reduced engine performance
Common Causes
- A faulty Manifold Absolute Temperature (MAT) sensor itself. These sensors can fail internally over time.
- Corroded or damaged electrical connectors leading to the MAT sensor. Always inspect these closely.
- A short circuit to ground or an open circuit within the MAT sensor's wiring harness. This can happen from rubbing or rodent damage.
- A damaged or improperly seated O-ring or gasket on the MAT sensor, which can cause a vacuum leak and affect readings.
- Less commonly, a fault within the Powertrain Control Module (PCM), though this is usually a last resort diagnosis.
Frequently reported on: Chrysler 300 (2005-2010), Dodge Charger (2006-2010), Dodge Ram 1500 (2002-2008), Jeep Grand Cherokee (2005-2010), Dodge Stratus (2001-2006)
Diagnostic Steps
- First, you'll need to locate the Manifold Absolute Temperature (MAT) sensor. On many Chrysler vehicles, it's typically threaded into the intake manifold or sometimes found in the air intake ductwork. Take a moment to visually inspect the sensor and its surrounding area for any obvious damage.
- Before you do anything else, disconnect the negative battery terminal. This is a crucial safety step and prevents electrical issues.
- Carefully unplug the electrical connector from the MAT sensor. These connectors usually have a locking tab or clip that you'll need to depress or slide before pulling it off. Be gentle, as old plastic can be brittle.
- Using an appropriately sized wrench or socket, unthread the old MAT sensor from its mounting location. Note how it's oriented as you remove it.
- Before installing the new sensor, make sure the new O-ring or gasket is properly seated. This ensures a good seal and prevents air leaks that could give you other problems. Apply a thin layer of dielectric grease to the electrical connector pins to help prevent corrosion in the future.
- Thread the new MAT sensor into its mounting hole by hand first to avoid cross-threading. Once it's hand-tight, use your wrench or socket to tighten it to the manufacturer's specified torque. Overtightening can damage the sensor or the manifold.
- Reconnect the electrical connector, making sure it clicks securely into place. You should feel it lock.
- Finally, reconnect the negative battery terminal. Once connected, start the vehicle and let it idle for a few minutes. The Check Engine Light should turn off after a few drive cycles if the repair was successful.
👨🔧 When to Call a Professional
If after inspecting the sensor and its wiring, you find no obvious issues like frayed wires or loose connections, or if replacing the sensor doesn't resolve the code, it might be time to call in a professional. A technician can perform more advanced diagnostics, like checking the wiring for continuity and resistance, or even testing the PCM's input, to pinpoint a more complex issue. Sometimes, what seems like a simple sensor problem can actually be a wiring harness or even an ECM issue. Don't just keep replacing parts if the code persists.
Commonly Asked Questions
What exactly does the Manifold Absolute Temperature (MAT) sensor do?
The MAT sensor measures the temperature of the air entering the engine's intake manifold. This information is vital for the engine's computer (PCM) to calculate the correct air density and, consequently, how much fuel to inject for optimal combustion. Think of it as telling the engine how 'thick' or 'thin' the air is.
Will a bad MAT sensor prevent my car from starting?
A faulty MAT sensor might not completely prevent your car from starting, but it can make starting very difficult, especially in extreme temperatures. Since the PCM isn't getting accurate air temperature data, it might inject too much or too little fuel, making it hard for the engine to ignite properly. It will definitely affect drivability.
Can I drive with a P1118 code?
While you might be able to drive with a P1118 code, it's generally not recommended for an extended period. The engine's fuel mixture will be off, leading to decreased fuel economy, potential power loss, and possibly increased emissions. Continued driving could also lead to other issues, like catalytic converter damage, if the engine runs too rich for too long. It's best to address it promptly.
Is the MAT sensor the same as the IAT (Intake Air Temperature) sensor?
Yes, for diagnostic purposes in many Chrysler applications, the terms MAT (Manifold Absolute Temperature) and IAT (Intake Air Temperature) are often used interchangeably, and they perform the same function: measuring the temperature of the incoming air. The specific naming might vary by manufacturer or sensor location (e.g., in the manifold vs. in the air intake tube).
After replacing the sensor, do I need to clear the code?
Yes, after replacing the MAT sensor, it's a good practice to clear the P1118 code using an OBD-II scanner. While the code might eventually clear itself after a few drive cycles if the problem is resolved, manually clearing it ensures the PCM resets its learned values and starts fresh. This allows you to confirm immediately if the repair was successful.